The present invention relates to the technology for removing residual ink and debris from an imaging surface of a printing system and more particularly to the cleaning of such residual ink and debris from the back of an imaging belt.
Modern high speed and high quality printers require great precision in spacing tolerances and alignment within key imaging subsystems. Such precision is particularly important within the image development subsystem of electrostatographic imaging systems where toner ink is transferred from a donor element to a latent image characterized by differential charges on an imaging surface. Any significant variation across the imaging width in the gap between the donor element and the imaging surface results in irregular image density and in other imaging defects. Where the imaging surface comprises a flexible endless belt moving in relation to the donor element, maintaining precise tolerances is particularly difficult. In response, backer bars or other web guide members are commonly used to provide, support, tension, and precise alignment and tolerances of the belt as it moves through key imaging subsystems, including the development subsystem.
Even with precisely placed and aligned backer bars, experience has shown that residual toner and debris that collects on the back of a moving photoreceptor or other imaging surface can sufficiently distort tolerances to introduce imaging anomalies. Such residual toner and debris results from toner that escapes from the development subsystem or from a primary or secondary cleaning system, from toner shaken off the image surface or copy substrates, or from paper fibers and other debris that enters the system with copy substrates. Although much care is made to inhibit such toner and debris and to collect it as much as possible, some toner and debris escapes and is attracted to the back of the imaging belt, particularly when the back of the belt carries an electrical charge. Although the total amount of toner and debris is small, it can eventually accumulate on surfaces contacted by the back of the belt. Such surfaces include, without limitation, backer bars and other web guide members. After enough accumulation in critical areas, required tolerances and alignments can be lost. This is particularly true with newer toner development systems such as hybrid scavengeless development (HSD”) and hybrid jumping development (“HJD”) systems. In these systems, toner is made to form a cloud of charged toner particles within the development gap. Toner particles are attracted out of such cloud toward the image areas on the imaging surface, which are oppositely charged. Toned images are thereby formed on the image surface. If the backer bars, which set the development gap between the photoreceptor and the donor elements, accumulate any significant amount of toner or debris, then the precise tolerances required across the entire image width of the gap are lost, and imaging defects result.
Among the various methods that might be considered for cleaning the inside of an imaging belt are rotating cylindrical brushes similar to those that are used to clean residual toner and debris from the imaging surface itself. The following references disclose various aspects of imaging surface cleaning systems that may be relevant to back of the belt cleaning systems, and the following references are hereby incorporated herein by reference in their entirety:
U.S. Pat. No. 2,832,977, discloses a rotatable brush mounted in close proximity to the photoreceptor surface to be cleaned and the brush is rotated so that the brush fibers continually wipe across the photoreceptor. In order to reduce the dirt level within the copier, a vacuum system is provided which pulls loosely held residual toner from the brush fibers and exhausts the toner from the copier. To assist the vacuum system in removal of the residual toner, the brush fibers are treated with a neutralizing ion spray from a corona generating device. This ion spray is intended to negate any triboelectrification generated when the brush wipes across the photoreceptor surface. Unfortunately, the brush becomes contaminated with toner after extended usage and has to be replaced more frequently than desired. With increased processing speeds of copiers and printers, the foregoing brush cleaning technique is not practical without improvements.
U.S. Pat. No. 3,722,018 discloses a more efficient residual toner cleaning system by positioning a corona generating device in the residual toner cleaner of U.S. Pat. No. 3,572,923 to induce a charge on the brush fibers and toner thereon of a polarity opposite that of a biased transfer roll, so that the toner collected by the brush are efficiently transferred from the brush to the roll. U.S. Pat. No. 3,780,391 discloses that toner removal from the brush can also be accomplished by the use of an electrically biased flicker bar.
U.S. Pat. No. 4,435,073 discloses a rotatable cylindrical brush cleaning apparatus for removing toner particles from a photoconductive surface. The brush is supported for rotation in a housing. The housing has an opening confronting the photoconductive surface and an aperture communicating through a conduit with a vacuum source. The brush extends from the housing opening into contact with the photoconductive surface. A plurality of flicker bars are mounted in the interior of the housing and in an air stream created by the vacuum source. The flicker bars are fabricated from materials which will not only cause the brush fibers to become electrostatically charged through wiping contact with the bars, but will cause the charge on the brush to reverse at least once for each revolution of the brush.
U.S. Pat. No. 4,851,880 discloses a rotating cylindrical brush and vacuum cleaning apparatus for removing toner particles from an image-bearing surface of a copier or printer. A housing that surrounds and substantially encloses the brush has an open portion adjacent the image-bearing surface. The brush extends through the open portion of the housing and into engagement with the image-bearing surface. The rotation of the brush is in a direction opposite to the direction of movement of the image-bearing surface. An elongated slot is located in the housing generally opposite the open portion and connects the interior of the housing to a vacuum source. Adjacent to the slot and on the interior of the housing is an airfoil to compress the brush fibers as the brush rotates thereby to loosen the toner particles in the brush fibers collected from the image-bearing surface. This loosening of the toner particles allows the vacuum to extract the toner particles through the housing slot. In an alternate embodiment, an additional airfoil of equal size is provided on the opposite side of the slot. The two airfoils compress the brush fibers on both sides of the slot and forces the air stream generated by the vacuum source to flow through brush fibers from opposite directions prior to exiting the housing through the slot.
U.S. Pat. No. 5,315,358 discloses one or more rotatable cylindrical brushes mounted in a housing having an opening therein to enable the brush or brushes to extend therefrom and into contact with a moving photoconductive surface to remove toner particles therefrom. A flicker bar is removably mounted within the housing and has an integral air channel therein. A vacuum source connected to the air channel in the flicker bar withdraws air and particles from the brush and housing. The solitary construction of the flicker bar provides a properly sized air channel that does not vary due to assembly tolerances.
Counterbalanced against the need to remove residual toner and debris is the need to make any cleaning system work within the extremely tight confines of the space within the belt loop itself. This space inside the belt is generally consumed by rollers, drive devices, supporting frames, etc. It is undesirable to lengthen the belt in order to add additional subsystems since such increase in belt size leads to increased size, cost, and weight of the overall printing system itself. Additionally, each additional subsystem and part within adds complexity and cost.
Another consideration when designing a back of the belt cleaning system is control of static charge build-up on the back of the imaging belt. Since the photoreceptor contains at least one insulating layer, charges can build on the back of the belt without being removed by the charging and discharging that occurs during the imaging cycle on the imaging side of the belt. Accordingly, it is common to utilize a static electricity removal device such as a grounded conductive brush. The static removal device typically does not cover the entire width of the belt but instead covers only a sufficient width to remove enough charge to prevent harmful static charge build-up. Even if such a grounded brush or other conductor covered the entire width, such passive grounding is believed to leave some irregularly spaced charges on the back of the belt due in part to the role that the insulating layer(s) of the belt play in preventing rapid conduction of charge from the belt to ground. Uneven electrical charge on the back of the belt is believed to affect the uniformity of charge attainable on the front of the belt.
Accordingly, it would be desirable to develop an effective, relatively low cost and compact system for cleaning residual toner and debris from the inside of an imaging belt. It would also be desirable to develop a system for uniformly removing charges from the back of an imaging belt such as a photoreceptor belt.
One embodiment of the invention is a brush cleaner assembly for cleaning the back side of an imaging web having a width, comprising: a support structure located proximate to the back side of the web; a brush rotatably mounted on the support structure in an interfering relationship with the back side of the web such that a substantial portion of the width of the back side of the web is swept upon rotation of the brush; and a drive device, coupled to the rotatable brush, for imparting rotational force to the rotatable brush.
Another embodiment of the invention is a method for cleaning the back side of an imaging web having a width, comprising: locating a support structure proximate to the back side of the web rotatably mounting a brush on the support structure in an interfering relationship with the back side of the web such that a substantial portion of the width of the back side of the web is swept upon rotation of the brush; and imparting rotational force to the rotatable brush.
Yet another embodiment of the invention is an electrophotographic printer comprising: a brush cleaner assembly for cleaning the back side of an imaging web having a width, said cleaner assembly comprising a support structure located proximate to the back side of the web; a brush rotatably mounted on the support structure in an interfering relationship with the back side of the web such that a substantial portion of the width of the back side of the web is swept upon rotation of the brush; and a drive device, coupled to the rotatable brush, for imparting rotational force to the rotatable brush.